A Light-Emitting Diode (LED), as used herein, is a semiconductor light source for generating light at a specified wavelength or a range of wavelengths. LEDs are traditionally used for indicator lamps, and are increasingly used for displays. An LED emits light when a voltage is applied across a p-n junction formed by oppositely doping semiconductor compound layers. Different wavelengths of light can be generated using different materials by varying the bandgaps of the semiconductor layers and by fabricating an active layer within the p-n junction. Additionally, an optional phosphor material changes the properties of light generated by the LED.
Traditionally, LEDs are made by growing a plurality of light-emitting structures on a growth substrate, usually sapphire. The light-emitting structures along with the underlying sapphire are separated into individual LED dies and packaged separately. The inclusion of sapphire with the packaged LED is a significant portion of the overall material cost. In some cases, the sapphire substrate is first separated from the light-emitting structure by a laser liftoff process; however, the reusability of the sapphire substrate is limited and the process can damage the light-emitting structure.
Continued development in LEDs has resulted in efficient and mechanically robust light sources that can cover the visible spectrum and beyond. These attributes, coupled with the potentially long service life of solid state devices, may enable a variety of new display applications, and may place LEDs in a position to compete with the well entrenched incandescent and fluorescent lamps. However, improvements in manufacturing processes to reduce the cost of making LEDs continue to be sought.